1. Field of the Invention
This invention relates to a method of establishing a connection between two endpoints in a communications network such that the connection provides a pre-specified quality of service for a specified communication session. The invention also relates to a communications network within which this method is implemented and also to a computer program for controlling a communications network in order to implement the method.
2. Description of the Prior Art
A current issue in the field of communications networks is the provision of guaranteed quality of service for transmission of internet protocol traffic. Quality of service is an important factor; customers require a good quality of service for message transmission especially for real-time applications such as video conferencing and voice. As well as this many customers require a particular level of quality of service to be guaranteed; if quality of service drops below a certain level and transmission is interrupted or noisy this may be acceptable in some situations but unacceptable in others. If particular levels of quality of service can be guaranteed this is particularly advantageous.
One approach that has been used is to prioritise individual transmissions that are sent over the network. For example, a system known as xe2x80x9cDiffServxe2x80x9d allows messages to be marked to indicate their priority. Nodes in a communications network are then arranged to process high priority messages first. This enables high priority messages to be processed quickly but it does not provide a guaranteed level of quality of service.
Another approach has been to reserve bandwidth over a particular route in a communications network. However, systems that use this approach (for example RSVP Resource reSerVation Protocol) typically are poor at implementing aggregation mechanismsxe2x80x94for example they cannot easily combine a number of separate sessions over the same route, each must have its own reservation. Another shortcoming is that they also typically only allow the called party to reserve bandwidth that is required to host a communication session. This does not allow the calling party to specify their requirements and this is problematic, especially because the calling party is typically the party which incurs costs for a call.
Multi Protocol Label Switching (MPLS) is a standard messaging protocol that is suitable for carrying Internet Protocol traffic over communications network s such as Asynchronous Transfer Mode (ATM) networks and Frame Relay networks.
Constraint-based Routing Label Distribution Protocol (CR-LDP) is also a standard messaging protocol (CR-LDP is defined in Internet Draft: draft-ietf-mpls-cr-ldp-01.txt) that is suitable for use with communications networks that use MPLS. Mechanisms such as CR-LDP allow MPLS the ability to set-up paths between two endpoints over a list of routers, where these paths have ATM-like traffic requirements. However, there is no well-defined mechanism for the choice of the routers in this path that makes full use of the ATM-like traffic parameters. The only existing mechanism (QOSPF Quality of Service Open Shortest Path First) allows routing only in terms of advertised router speed and congestion. In tandem, QOSPF is unable to make the fullest use of CR-LDP as it cannot make use of the detailed traffic descriptions used in CR-LDP; neither can it provide detailed route information. As well as this QOSPF is not able to ensure a connection over a suggested route.
It is accordingly an object of the present invention to provide a method of establishing a connection between two endpoints in a communications network, such that the connection provides a pre-specified quality of service, for a specified communication sesion, which overcomes or at least mitigates one or more of the problems noted above.
Further benefits and advantages of the invention will become apparent from a consideration of the following detailed description given with reference to the accompanying drawings, which specify and show preferred embodiments of the invention.
According to an aspect of the present invention there is provided a method of establishing a connection between two endpoints in a communications network such that a specified level of quality of service is given for a specified communication session using the established connection, said method comprising the steps of:
(i) determining a plurality of possible paths between the endpoints;
(ii) determining a measure of preference for each of said possible paths on the basis of information about the communications network and information about the specified communication session;
(iii) reserving bandwidth along the most preferred path according to said measures of preference; and
(iv) establishing a connection over said most preferred path.
A corresponding communications network is provided comprising at lea:3t two endpoints between which it is desired to establish a connection such that a specified level of quality of service is given for a specified communication session, said communications network comprising:
(i) a processor arranged to determine a plurality of possible paths between the endpoints;
(ii) a determiner arranged to determine a measure of preference for each of said possible paths on the basis of information about the communications network and information about the specified communication session;
(iii) a reservation mechanism arranged to reserve bandwidth along the most preferred path according to said measures of preference; and
(iv) a connection mechanism arranged to establish a connection over said most preferred path.
A computer program stored on a computer readable medium is also provided, said computer program being for controlling a communications network comprising at least two endpoints, said computer program being arranged to control said communications network such that:
(i) a plurality of possible paths between the endpoints is determined;
(ii) a measure of preference for each of said possible paths is determined on the basis of information about the communications network and information about a specified communication session;
(iii) bandwidth is reserved along the most preferred path according to said measures of preference; and
(iv) a connection over said most preferred path is established such that a specified level of quality of service is given for the specified communication session.
This provides the advantage that a communications session is established which has a guaranteed quality of service. Switch virtual circuit equivalency is effectively given for a communications network which can be an internet protocol based communications network such as an MPLS network.
Preferably, said step (ii) of determining a measure of preference for each of said possible paths further comprises the steps of:
(i) for each of said possible paths, determining a first set of measures of preference on the basis of information about a region of the communications network around a first one of the two endpoints; and
(ii) for each of said possible paths, determining a second set of measures of preference on the basis of information about a second region of the communications network around a second one of the two endpoints.
This provides the advantage that information about the communications network is only required for two regions of the communications network; this simplifies the method and enables it to operate quickly.
Preferably, said communications network comprises a plurality of nodes connected together by links and said method further comprises the step of configuring the communications network such that the links between a first plurality of nodes are of a pre-determined capacity such that in use each of said links between the first plurality of nodes is capable of sustaining a plurality of separate communication sessions. By provisioning the communications network in this way high capacity routes which act as xe2x80x9cmotorwaysxe2x80x9d are created. By using these high capacity routes, the topology information required to implement the method is reduced. This simplifies the method and makes it faster to operate.
According to another aspect of the present invention there is provided, an entity for use in a communications network comprising at least two endpoints between which it is desired to establish a connection such that a specified level of quality of service is given for a specified communication session, said entity being associated with one of said endpoints and comprising:
(i) a memory containing information about the topology of at least part of the communications network;
(ii) an input arranged to receive a request for a specified communication session;
(iii) an output arranged to issue a plurality of request messages in response to a request for a specified communication session; each of said request messages comprising information about the specified communication session.
For example said entity may be an admission manager. The entity provides a means by which request messages may be issued, each with its own measure of preference, in order to implement an improved SIP type method described herein.
According to another aspect of the present invention these is provided an entity for use in a communications network comprising at least two endpoints between which it is desired to establish a connection such that a specified level of quality of service is given for a specified communication session, said entity being associated with one or more nodes in said communications network and comprising:
(i) a monitor for monitoring the available bandwidth in each of the links emanating from said associated nodes; and
(ii) an advertisement mechanism for advertising said monitored available bandwidth.
For example, the entity may be a connection manager. The entity provides a means by which traffic levels in the network are advertised and this helps to implement an improved SIP type method described herein.